copper tube mechanical pencil

this is a mechanical pencil i made to fit 10 mm od by 7mmish od coper tube about 156mm long tube, it works by shaking the pen to make the 3mm hole marking graphite move out.
it requires a spring and a metal slug about 49mm x 6mm.
please note this is a prototype made out of wood and scrap metal. ill update this when i get the parts printed. update: i printed the parts and super glues the tip in, i think the tube may need to be slightly longer because its hard to work when the graphite is all th